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The Johnston County Osteoarthritis Project: Arthritis & Disability

Project Description

This project is a unique, community-based, longitudinal study of approximately 3200 rural white and black residents aged 45 and older. It is designed to determine the prevalence, incidence, and risk factors associated with the occurrence and progression of hip and knee osteoarthritis (OA)—the most common and disabling types of arthritis. Results of this study will allow a better understanding of how and why these conditions occur and what modifiable risk factors can be targeted to reduce their impact. This project implements surveillance and epidemiology strategies from the National Arthritis Action Plan—A Public Health Strategy which are a priority for the primary funding agency—the Center for Disease Control and Prevention’s (CDC) Arthritis Program. This project was previously supported by the CDC’s National Center for Environmental Health’s Office of Disability and Health and is currently also supported by the National Institutes of Health's National Institute of Arthritis and Musculoskeletal and Skin Diseases and National Institute of Mental Health.

Project Objectives

Determine the prevalence, incidence, and risk factors associated with the occurrence and progression of hip and knee osteoarthritis.

Determine racial or ethnic differences in outcome and in the effect of risk factors upon OA outcomes.

Key Findings

Time 1 (T1, Baseline) (1991-1998)—From 1991 to 1998 participants aged 45 years and older were enrolled in the project. Analyses published from this phase of the project have already demonstrated (1) a higher rate of osteoarthritis among African Americans than previously thought, (2) the importance of overweight in the development and severity of osteoarthritis among African Americans, particularly women, and (3) the importance of pain in determining functional limitations among persons with osteoarthritis. A recent publication demonstrates the high prevalence of four different measures of knee osteoarthritis (knee symptoms, modest and severe radiographic OA, and symptomatic knee OA). (2007)

As the only study of OA biomarkers to include African Americans, the study has been pivotal in this burgeoning field, demonstrating that (1) ethnic differences exist in multiple OA biomarkers, (2) some serum biomarkers may predict pre-radiographic OA, (3) body mass index, comorbid conditions, and medications can confound associations between some biomarkers and OA, (4) hormone replacement therapy (HRT) is associated with lower levels of several OA biomarkers, elucidating potential mechanisms behind the effect of hormone replacement therapy and OA, and (5) OA should be accounted for in relationships between C-Reactive Protein and cardiovascular disease. The study has also examined serum antioxidants as risk factors for OA and noted that higher levels of serum lutein, beta-cryptoxanthin, and the ratio of alpha to gamma tocopherol were associated with lower odds of having knee osteoarthritis. The study is also the only human study examining metabolomics in OA, showing distinct urinary metabolite patterns that can distinguish those with OA from controls.

Time 2 (T2, First Follow-up) (1999-2004)—Analyses published from this phase of the project have already demonstrated (1) a higher rate of progression of osteoarthritis among African Americans than previously thought, (2) the importance of overweight in osteoarthritis among African American women, and the contributions of body composition and fat distribution in this relationship, and (3) higher odds of radiographic OA presence and severity in those with low levels of toenail selenium, a new and potentially modifiable risk factor for OA.

Studies in Johnston County, NC, have found the following:

Nearly 1 in 2 people may develop symptomatic knee OA by age 85 years

Two in three people who are obese may develop symptomatic knee OA in their lifetime.

1 in 4 people may develop painful hip arthritis in their lifetime.

Time 3 (T3, Second Follow-up) (2005-2010)—Data collection for this phase is continuing. Analyses published from this phase of the project have examined disability, function, mortality, racial differences in radiographic evidence of disease, racial differences in willingness to undergo total joint replacement, and the effects of socioeconomic status on arthritis outcomes.

Time 4 (T4, Third Follow-up) (2011-2015)—Data collection for this phase is continuing.